This invention relates to an improvement on a ventilated-type disc rotor to be used for a braking system of a vehicle.
In a conventional ventilated-type disc rotor such as the one as disclosed in Japanese Patent Laid-open No. 2-253020 and illustrated in FIGS. 16 and 17 of the accompanying drawings, a disc rotor which is generally designated by reference numeral 1 in these figures comprises an internal disc 2 and an external disc 3 disposed in a face-to-face relationship with a number of ribs 4 radially arranged between the discs to provide pathways 5 for cooling air defined by any two adjacent ribs so that the two discs are frictionally pressed against each other by way of a brake pad for braking the vehicle and the heat generated on the frictional surfaces of the discs is moved away from there with the air to cool the heated discs.
The external disc 3 is connected at its inner periphery to a cylindrical member 6, which is by turn connected to the outer periphery of a fitting plate 7 that constitutes a flange to be secured to the vehicle main body. Said fitting plate 7 is provided with a central bore 8, fitting holes 9 and auxiliary holes 10 arranged for making the operation of removing said disc rotor from the vehicle main body be carried out without difficulty.
A known ventilated-type disc rotor as described above is accompanied by a drawback of presenting a phenomenon of thermal deformation of the internal and external discs 2 and 3, which is typically illustrated by broken lines in FIG. 18, due to the heat generated on these discs 2 and 3 particularly when the vehicle is braked while the wheel shafts are rotating at an enhanced rate or when the vehicle is braked frequently within a short period of time.
A large internal stress becomes present in the external disc 3 as such a phenomenon takes place, leading to generation of radial cracks as typically indicated by C1 and C2 in FIGS. 19 and 20. Besides, as the discs are thermally deformed, the abutment (contact) of the brake pad and the disc rotor 1 becomes unstable and a so-called brake jadder phenomenon that fluctuates the braking effect of the brake can occur.